The present invention relates to millimeter wave devices, and more particularly, imaging devices that utilize scanned millimeter waves.
Millimeter wave devices promise many useful applications, because such devices provide a small solution to many local transmission applications. Moreover, millimeter wave devices may be useful in detecting objects behind optically opaque barriers, much like X-rays. Advantageously, millimeter wave devices can take advantage of many optical techniques, such as focusing lenses and reflectors. This capability provides flexibility in developing small components with unique capabilities.
One application of millimeter wave devices is for imaging through opaque materials, such as concrete walls and plastic boxes. Conventional millimeter wave imaging devices utilize highly sensitive detectors fed by fixed waveguides. To image a target object, the entire device is moved until the waveguide is aligned to the target object. The waveguide then collects millimeter wave energy emitted or reflected by the target object and directs the millimeter wave energy to the detector.
Typically, the field view of the waveguide is quite small. Consequently, the portion of the target object that can be image at any one time is quite small. Imaging the entire target object can therefore involve moving the entire device through a series of many orientations. At each location, the millimeter wave energy is sampled and stored. Gradually, an entire data set is built up. From the data set, signal processing can produce an image of the target object.
One difficulty with this approach is the time required to generate the entire data set. Gathering data in this fashion can be tedious and costly.
This difficulty becomes particularly problematic where the target object is moving. In such a circumstance, the time lag between data taken for a first orientation and data for a second orientation may be sufficiently large that the target object may move significantly during the time lag. The final data set may represent portions of the image taken for different positions of the target object. Consequently, the data set may represent a highly distorted image of the target object.
A millimeter wave scanning imager scans an image field to collect millimeter waves from an external environment. A sensitive detector monitors the millimeter wave energy received from the external environment and produces an electrical signal indicative of the energy received. An electronic controller samples the electrical signal to produce image data corresponding to the scanned millimeter wave energy.
Because the electronic controller concurrently monitors the scan position, the electronic controller can determine the corresponding location in the external environment for producing the image data. Accordingly, the electronic controller can build an image data set representative of the external environment.
In one embodiment, the imager includes a scanner that scans one or more reflectors through a periodic two-dimensional scan pattern. The scan pattern may be a raster pattern or another type of pattern, such as a vector or spiral pattern.
One embodiment of the scanner is a microelectromechanical (MEMs) scanner. The MEMs scanner is a biaxial scanner having a central reflector coated with a conductor.
In another embodiment, the scanner includes two mechanically resonant scanners driven by electromagnetic coils. The central reflectors of the scanners formed from a metal that reflects the millimeter wave energy.
To improve the sensitivity, the imager also includes dielectric lenses that gather and focus the millimeter wave energy onto the detector. One embodiment also includes additional dielectric lenses with variable positioning to adjust the imaging distance of the imager.
To improve the detector sensitivity, the imager also includes a super cooler that cools detector to a very low temperature. The very low temperature reduces the detector noise to improve the signal to noise ratio of the imager. Consequently, the imager does not require an illuminating millimeter wave source.
Because the millimeter wave imager is formed from small components, including a small super cooler, and does not require a separate source, the imager may be small and light enough to be human portable.